conventionally, a cumbersome trial and error process must be used to design a light guide such that the light guide's light emitting surface will be uniformly illuminated. Typically for example a light guide having desired dimensions is constructed and operated to determine the uniformity with which light is emitted at different points on the emitting surface. The light guide's light extraction mechanism, which may take various forms, as noted, for example, in U.S. Pat. No. 4,787,708 Whitehead "Apparatus For Continuously Controlled Emission of Light From Prism Light Guide", is then altered in a manner which is expected to improve the light guide's uniformity of illumination. The foregoing steps are repeated until an acceptable degree of uniformity is attained.
The foregoing prior art technique results in a light extraction mechanism which can be reused only in light guides having the same dimensions as the light guide for which the extraction mechanism was developed. If the same extraction mechanism is used in a new light guide having substantially different dimensions then it is a very likely that the new light guide will not emit light with the same degree of uniformity as the light guide for which the extraction mechanism was developed.
It is most typical to vary the length dimension of a light guide to suit different applications, and considerably less typical to vary the light guide's other dimensions. The present invention facilitates construction of a light extraction mechanism for a "standard" light guide of predetermined maximum length having a desired uniform light output characteristic. Shorter light guides, each having the same uniform light output characteristic as the standard light guide (but having different brightness characteristics, due to the inverse relationship of light guide length and brightness), can be constructed by removing from the appropriate end of a light extraction mechanism identical to that required for the standard light guide, a segment equal to the desired length of the shorter light guide. This obviates the need for cumbersome trial and error development of a different light extraction mechanism for each such shorter light guide. The invention also facilitates construction of a modular light guide having a length which can be a multiple of a standardized unit length, such that the light guide's light output uniformity remains constant, irrespective of the length of the light guide.